 |
| Titel |
Evolution of Fourier spectra through interplanetary shocks |
| VerfasserIn |
Alexander Pitna, Jana Safrankova, Zdenek Nemecek, Frantisek Nemec, Oleksandr Goncharov |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250087567
|
| Publikation (Nr.) |
 EGU/EGU2014-1622.pdf |
|
|
|
|
|
| Zusammenfassung |
| Well established nearly isothermic solar wind expansion requires an additional heating. A
dissipation of large scale variations of the solar wind kinetic energy into the thermal energy
via turbulence cascades is thought to be an important source of this heating, although the
exact mechanism is yet to be found. For this reason, the turbulence in the solar wind is a
subject of extensive theoretical and experimental studies on different time scales ranging
from years to minutes. The frequency spectrum of magnetic field fluctuations can be divided
into several domains differing by spectral indices — the lowest frequencies are controlled by
the solar activity, MHD activity shapes the spectrum at higher (up to 0.1 Hz) frequencies,
whereas the ion and electron kinetic effects dominate at the high frequency end of the
spectra.
Interplanetary shocks of various origins are a part of solar wind turbulence naturally
occurring in the solar wind and the BMSW instrument onboard the Spektr-R spacecraft has
detected tens of them in course of the 2011–2013 years. Based on its high-time resolution of
the ion flux, density and velocity measurements reaching 31 ms, we study an evolution of the
frequency spectra on MHD and kinetic scales across fast forward low Mach number
shocks.
We have found that the power of downstream fluctuations rises by an order of
magnitude in a broad range of frequencies independently of its upstream value
but the slope of the spectrum on the kinetic scale (-3–8 Hz) has been found to
be statistically steeper downstream than upstream of the shock. The time needed
to a full relaxation to the pre-shock spectral shape is as long as several hours. A
combination of the ion flux power spectra obtained by BMSW with fast magnetic
field observations of other spacecraft enhances our understanding of dissipation
mechanisms. |
|
|
|
|
|
|